黄河水系沉积物碎屑矿物组成及沉积动力环境约束

黄河水系河漫滩沉积物的碎屑矿物组成研究表明,主要支流和干流沉积物中碎屑矿物组合基本相似,不同支流和干流不同河段的矿物含量不同,具有一定的区域分布规律。重矿物主要组合为不透明矿物-石榴子石-绿帘石-碳酸盐矿物和蚀变矿物。轻矿物的物源区指数难以可靠地反映黄河主要支流和干流不同河段碎屑矿物的物源差异;轻矿物成熟度指数在不同水系间的变化较复杂,中游沉积物低于上游与下游平原沉积物,它既体现沉积物物源的控制,又反映河流泥沙输运及沉积过程中的分选性差异。石榴石、不透明矿物及角闪石的含量变化主要反映悬浮泥沙的沉积分异程度以及不同水系的水动力强度。重矿物ZTR指数的区域分布特征一定程度上反映出不同沉积物的物源区分布。重矿物分异指数F清晰地揭示出由于区域水动力强弱变化导致特征碎屑矿物组成的沉积分异,因而,可作为研究单物源河流沉积动力环境和碎屑矿物沉积分异程度的指标。总体上,黄河碎屑矿物的含量变化并不完全受物源控制,而更主要地反映季节性的河流水动力强度与沉积环境差异,以及由此引起的碎屑矿物的重力分选作用,因此,在边缘海区运用碎屑矿物组成识别黄河入海物质的贡献时需谨慎。

DETRITAL MINERAL COMPOSITION OF THE SEDIMENTS FROM HUANGHE AND ITS HYDRODYNAMIC ENVIRONMENTAL CONSTRAINTS

The composition of detrital minerals of the sediments from Huanghe mainstream and major tributaries are similar in general, albeit certain variation between different rivers. The main assemblages of heavy minerals are opaque minerals-garnet-epidote-carbonate and altered minerals. It is difficult to delineate the source area by using the source index of light minerals. The maturity index of light minerals also shows very complicated variations between different river samples, reflecting the combined controls of the sediment sources and sorting process during transportation and deposition. It is lower in the middle mainstream than in the upper and the lower reaches. The variations of garnet, opaque minerals and hornblende contents obviously suggest the differentiation of suspended loads and hydrodynamics changes of rivers. The regional distribution of ZTR index well corresponds to the provenance of the river sediments. A dif-ferentiation index was proposed in this study to reveal the differentiation of characteristic minerals caused by regional hydrodynamic sorting. The index can be used as a good indicator for study of sedimentary hydrodynamic environment and differentiation of detrital minerals. As a whole, the mineral compositions are not only controlled by their sources, but also constrained by seasonal hydrodynamic intensity of the river and the mineral gravity differentiation induced by sedimentary environment changes. It should be careful to identify sediment sources in the marginal sea just based on the mineral assemblages of the river,such as Huanghe.